Fibrous glass articles



Patented Jan. 10, 1950 2,494,259 FIBROUS GLASS ARTICLES Martin EmeryNordberg, Corning, N. Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York No Drawing. Application'March 20, 194.6,Serial No. 655,891

8 Claims. (01. 106 50) This invention, which is a continuation in partof .my' pending application S. N. 519,831 filed J anuary 26,1944,.andissued February 15, 1949, as Patent No.- 2,461,841, relates tothe manufacture of glass fibres and it is particularly concerned withthe treatment. of. glass fibres and fabrics thereof wherebynon-siliceous constituents are removed from the fibres by a leachingprocess to produce highly siliceous fibres and fabrics of novelcompositions having improved character istics.

Recent advances in the art of spinning glass and the development of anever Widening field of uses forwovenand unwovenifabrics and textiles offibrous glass have led to the need for still furtherimprovements'in'their methods of production and the compositions andphysical characteristics of the fibres. The known methods of producingglass fibres economically in largequantities place certain limitationson the types and compositions of glasses which can be employed and thusalso on the compositions and physical characteristics of thefibres whichcan be produced. Glasses which are adapted for the production ofarticles of relatively large mass, suchv as utensils of all sorts,electrical insulators, and the like, having the characteristics of highthermal'endurance, highchemical durability, high electrical resistance,low power factor, and other desirable properties are often times totallyunsuited for spinning into fibres. Some of the causes for suchunsuitability are: too high melting temperatures, too high viscositiesat the melting temperatures, objectionable alkalinity, tendency to formslugs or shot? in the blowing process, or tobreak the continuous fibrein the drawing method, etc.

The primary object of this invention is to form glass fibres fromcompositions, which are easy to L Work and thereafter to convert thefibres to a different composition by leaching out at least some of thefluxes used in melting the glass.

Another object isto produce glass fibres having novel compositions. I

Another object is to produce glass fibres of high chemical durability,particularly toward acids.

Another object is to produce glass fibres composed of silica andrefractory oxides.

Another object is toproduce glass fibres havinga high sorptive capacity.s

Another object is to produce porous glass fibres.

Another object is to produce porous glass fibres of high silica content.H v

Another object is to produce porous fibres of 2 practically pure silicawhich can be revitrified at low temperatures.

Anotherobject is. to produceglass fibres and felted and woven fabricsthereof which have heat resisting qualities asgood or better thanpresent materialsof this form. Another object is to produce a substitutefor asbestos. I

Another object is to produce a thermal insulation for high temperaturewuse.

Another object is to improve the electrical properties ,of glass fibresand fabrics thereof.

Another objectv isto produce glass fibres and fabrics which are softerto the touch than prior glass fibres and fabrics and which are lessirritating to the human skin.

Tonthese and other ends the invention comprises glass fibres, andfabrics composed thereof,

.having new and useful properties which render them particularlysuitable for various purposes, as will hereinafter be more fully setforth.

have found that the leaching of fibrous glass articles to extractnon-siliceous constituents, thereby changing, the'composition of theglass andat the same time producing strong fibrous articles, cannot beaccomplished in the manner and by the methods heretofore used in theleaching and,,revitrification of glass articles having relatively largemass, but must conform to the critical requirements and conditionshereinafter set forth... In the first place, the preliminary heattreatment which is ordinarily employed to condition the glass forleaching or to cause a separation or formation of a soluble phase orcomposition dispersed within the glass mass cannot be employed intreatingglass fibres. This is due to the fact that heating the fibres orfibrous materials for the necessary time at any temperature whichiseffective causes sintering and fusing of impermeable without apreliminary heat treatment or they crumble, and disintegrate on accountof breaking stresses set up in the glass dur ing leaching. Fibres whichhave diameters less than about .001 inch, on the other hand, can beleached. successfully because such stresses cannot becomeserious beforethe fibre iscompletely leached through. The use of fibres still smallerin diameter, say about .0003 inch, is advantageous not only because theleaching action is faster and the range of compositions which can beleached is broader than for fibres near .001 inch, but the weaving offabrics requires the use of the smaller fibres and the leaching andconsolidation of woven fabrics is an important feature of my invention,as will appear.

I have discovered that, subject to limitations as to composition, bothborosilicates and nonborosilicates can be leached inacid solutions toextract non-siliceous constituents when in the form of fibres havingdiameters less than about .001 inch. In contrast to this,non-borosilicates cannot be leached satisfactorily when in massive form.Glasses, the fibres of which can be leached in accordance with thisinvention, contain not over 75% SiOz, at least one glass flux consistingof. alkali metal oxide (R) or boric oxide, and

an oxide of one or more of the followingmetzpls: beryllium, magnesium,calcium, zinc, strontium, cadmium, barium, aluminum, titanium, zirconlumand thorium. During leaching the greater part, if not all, of the fiuxor fluxes is above; on the other hand, fibres composed of borosilicateglass having diameters less .than about .001 inch and containinglessthan about 70% S02 leach readily in acid solutions, such ashydrochloric acid.

Whenthe major portion of the non-siliceous constituents ofalkali-borosilicate glasses. forms water soluble compounds on leaching,such glasses can be leachedwith water. However, if the alkali content ishigh, the bath becomes alkaline, as leaching proceeds with a resultantattack on the silica structure of the fibres. .,To overcomethisdiificulty, acid must be added to the bath ,When the alkali to boricoxide ratio islow, say not more than about 1 to, 5, thesolution willremain essentially neutral 'and the addition of acid to the bath isunnecessary.

' When glass fibres composed of silica,-.boric oxide,,alkali metaloxide, and alumina, and n eetingthe above. stated requirementsas todiameter and, silica content, are leached with an acid solution, theultimate composition of the leached fibres is difierent from that of amassive article of thcsame glass heat treated and leached in the samemanner. An alkali borosilicate containingabout 2% A1203, when heattreated and leached in massive form, i. e., in a thickness substantiallygreater than about .001 inch, has an ultimate composition consisting ofover 96% S102, about 3%. 3203, with traces of A1203 and NazO, but whenthe same glass in the form of fibres having diameters less than .001inch is leached fibres of .001 inch diameter or less and the fibres wereleached for ten minutes in 1 Normal aqueous hydrochloric acid maintainedat 95 C. The leached fibres were thoroughly washed with water and dried.The resulting fibres on the dry basis had the composition 96.7% SiOz,3.1%

A1203, .2% B203, and 03% NazO, and were very soft and pliable.

Fibres composed of borosilicate glasses which are substantially freefrom alkali metal oxides, but which contain substantial amounts ofsecond group oxides and alumina, may also be leached but require an acidsolution because the major portion of the non-siliceous constituents arepractically insoluble in water. The initial glass should contain notmore than 56% S102, not more than about 22% total second group oxides,not less than about 12% A1203 and at least 5% E203. Such glasses haveproperties making them particularly suitable for drawing into glassfibres. The resulting fibresiafter leaching have a high silicacontent,90% to 99.5% $102, are free from alkali and contain up to 4% of alumina,up to 4% of second group oxides, and up to 4% B203.

Example 2 A roll of tape composed of glass fibres having washed withwater and dried. The final compositicn on thedry basis was about 90.5Si02,=3.5% A1203, 2.7% Cat), 3% MgO and-2.5% 1320a Fibres ofnon-borosilicate glass orglasses com- .posed ofsilica, alkali metaloxide, and second in the same manner, the ultimate composition of thefibres consists of over 96% SiOz, about 3% h1g0; with traces of B203 andNazO.

Example 1 A glass having the composition 62% S102, 8%

NazO, 28% B203, and 2% A1203 was drawn into group oxide, such as theoxides of beryllium,

-magnesium, calcium, zinc, strontium, cadmium and barium, and containingnot more than about SlO2, leach readily, provided their alkali contentis more than about 20%. Asthe silica content of such glasses isdecreased the minimum amount of alkali metal oxide which must be presentalso may be decreased somewhat. The final composition of such fibresafter leaching is to Si02, less than 10% second-group metal oxide (R0)and less than 1% alkali metal oxide (R20). As the leaching time isincreased the R0 and R20 contents of the fibres become smaller and thesilica content ultimately approaches 100%.

Example 3 Glass fibres having diameters less than .001 inch and composedof approximately 70% S102, 20% NazO and 10% CaO were leached for onehour in.1 Normal aqueous hydrochloric acid at 96 C. The leached fibreswere washed, dried and fired at 800 C. and had the approximatecomposition 93% SiO2 and 7% CaO.

Fibres having unusual compositions may be produced by means of myinvention, by including the refractory metal oxides 'IiOz, ZrOz, Th0:and A1203, which form acid insoluble components in the resultant glass.For example, glasses composed of silica, alkali metal oxide, andzirconium oxide, the total alkali metal oxide being not less than about25% and ZrO2 being not more than about 15%, when drawn into fibreshaving diameters less than .001 inch and leached with an acid solution,produce glasses which consist of silica and zirconia, and containingatrace of alkali metal oxide.

A gnSS' cmSiStingOr 61.9% S102, 28.6% NazO and 9.5% ZrOz was drawn.,into.-fibres.having diametersless than .001 inch, whichiwere thenleached for one hour with lNormal. aqueous hydrochloric acid at 96 C.and thereafter washed in pure water, .driedandlfired at,80.0 C.. .Thefibres were'then found to..be composed of about 88% SiOz, 12% ZiOz .and.25%.N.a2O..

A similar result may be obtained .Whenoxides of certain other .metals.of. the .fourth periodic group (R02) as titanium oxide or thorium oxideare substituted for zirconium. oxide: in; the .above glass. .The finalcompositions .of...the leached fibresiwill contain substantiallymoreSiOz and R02 and less R20 than.theoriginalglass.

.rn practicing. my invention,.it isessential that the leaching bath bemaintainedin a non-alkal'inelcondition, .i. e., .eitherneutral or acid.Aspointed out above, highlyacid glasses which contain .a large amount ofboric oxide, and little or no alkali metal oxide, may be leached withwater. In the case of highly basic glasses, such as glassescontaining ahigh percentageof alkali metal oxide or oxide ofa metal ,of the secondperiodic group, it is desirable toi use' a strong acid solution. Unlesssufficient acid is present in thebath to neutralize, all of the basicconstituents. of the glass, the bath-.may become alkalineandthe silicapfthefibres maybeflisve here a n t ei di i ra i On account of the smalldimensions of the fibres and the small depth to which the leachingaction must penetrate in order to permeate the fibres, the leaching timeis relatively short but may vary from ten minutes to an hour or more,depending upon the concentration of the acid in the leaching bath andits temperature. The speed of leaching, in general, may be increased byincreasing the acid concentration and/or increasing the temperature.When leaching is completed, the fibres should be thoroughly washed withpure water. A leaching time up to several hours is required forcompacted masses of fibres or exceedingly thick and tightly wovenfabrics, because the diffusion of the solvent into the mass becomesrelatively slow.

Glass fibres which have been leached in accordance with the methodsdescribed above are porous and have a somewhat lower tensile strengththan the original fibres as drawn. I have determined that the pores ofthe leached fibres are smaller than those occurring in porous glasseswhich have been leached in massive form. For this reason, despite theirsmaller capacity, water is more strongly retained in the porous glassfibres than in massive porous glass. I have found that the glass fibresretain about of their weight of water after being heated for severalhours at 150 C. A major proportion of this residual water can be removedby more drastic treatment, such as heating at 175 C. in vacuo. Theresultant material is a powerful dessicant.

I have discovered that such porous leached glass fibres can beconsolidated, i. e., revitrified or converted to non-porous vitreousglass fibres by heating them at temperatures well below the temperatureswhich are required to consolidate similar porous glasses in massiveform. Were it not for this fact, it would be diflicult to consolidatethe porous fibres without surface devitrification or sintering, whichwould seriously weaken the resultant fabric. Porous fibres composed ofapproximately 97% S102 and 3% A1203 become consolidated or non-porouswhen heated too? The ability to. consolidate at uphl low teniperatur esis compatible with the increased surface energy of the. porousfibres.

On accountof the novel characteristics 'ofsuch small dimensional glassfibres du'ring leaching and consolidationfl have found it highly,advantageous to first form the fibres into thefldesired woven ,orunwoven. "articles. before, leaching. Feltedor wovenglassifibres can be."ache'dand consolidated as readilyas individualfibres. vwith a greatsaving in'tima'material's ando'ver h'e ad costs.

It is customary, in the, spinningfof g lass to coat the' fibre's withfalubricantLsuclr' as.. anfoil, wax, or other greasy 3 or, unctuousEmater'ial.- inf order to prevent abrasion of the' fibrges during..sp'in ning and during their fabrication into woveln or unwoven fabricslhave found that such,coatingfs do not interfere substantially, .with;my .new process and that leaching and revitrificationiof the fibrescanbecarried out in, their, presence. However, such coating materia1s;..mammate are leachingbathgand leave an. organic, residue which, issrnetim'esv difficult to eliminate from theporous fibres duringsubsequentheat treatment and may cause discoloration of .thefiiialfibres. H enceit is usually preferableto renf'i ove the coating, eitherby heating thefabric at about 300 C. ;o r by treating'itQWith a solventbefore subjecting it, to, the leaching operation. As pointed out above,the unusually low temperature at which the porous fibres may beconsolidated despite their high silica content permits completeconversion of the fibres of the treated fabrics to a non-porouscondition Without sintering or fusing the fibres and without undue lossof tensile strength. If desired, the consolidated fibres or fabric maybe relubricated or coated with lubricant material after consolidation.

Fibres and fabrics thereof which have been leached and consolidated inaccordance with my invention are unique in their texture and softness ascompared to ordinary glass fibres and fabrics. The new fabrics areremarkably soft and pliant to the touch and feel more comparable to thefabrics composed of silk or cotton fibres than prior fibrous glassarticles. As a result of their high silica content, they also possessthe property of considerably higher heat resistance than prior glassfabrics and afford an excellent substitute for asbestos fabrics. The newglass fabric is stable at temperatures above 400 0., at

which asbestos dehydrates and disintegrates.' Consequently, the newfabric has been found to be very useful as an insulating material foruse at temperatures ranging from 400 C. to 1200 C. A further advantageresulting from their composition is the improved electrical resistanceand low power factor of the new glass fabrics which together with theirincreased heat resistance makes them still more desirable for theinsulation of wires and electrical conductors which are to be employedunder conditions of elevated temperatures, such as the windings ofelectric motors.

For some purposes it is desirable to omit the step of revitrificationand to leave the fibres porous. It has been found that the porous fibreshave strong absorptive powers for liquids and vapors. The porous fibresare therefore particularly useful in filters and selective absorptiondevices for the purification of air and other gases.

I claim:

1. An article comprising glass fibres which have a diameter less than.001 inch and which *7 consist approximately of 90.5%, Si02, 3.5% A1203,2.7% 02.0, 31% M'gO, and 2.5% 13202 the fibres being porous.

2. An article comprising glass fibres which have a diameter less than.001 inch and which consist approximately of 90.5% S102, 3.5% A1203,2.7% Ca(), 37% MgO, and 2.5% B203 the fibres being vitreous andnon-porous.

3. An article comprising glass fibres which have a diameter less than.001 inch and which consists essentially of at least 88% Si02, theindicated amount of at least one glass flux selected from the groupconsisting of up to 1% alkali metal oxide and up to 4% B203, and atleast one additional glass-forming oxide in the indicated amountselected from the class consisting of up to 10% BeO, up. to 10% MgO, upto 10% CaO, up to 10% ZnO, up to 10% SrO, up to 10% CdO, up to 10% BaO,up to 4% A1203, up to 12% Ti02, up to 12% D02 and up to 12% Th02, thefibres being porous.

4. An article comprising glass fibres which have a diameter less than.001 inch and which consists essentially of at least 88% SiOz, theindicated amount of at least one glass flux selected from the groupconsisting of up to 1% alkali metal oxide and up to 4% B203, and atleast one additional glass-forming oxide in the indicated amountselected from the class consisting of up to 10% BeO, up to 10% MgO, upto 10% 0210, up to 10% ZnO, up to 10% SrO, up to 10% CdO, up to "8 10%32.0, up to 4% A1203, up to 12% TiOz, up to 12% Zl'Oz and up to 12%T1102, the fibres being vitreous and non-porous.

5. An article comprising glass fibres which have a diameter less than.001 inch and which consist of SiOz containing 3.1% A1203, .2% 13203 and.03% Na2O, the fibres being porous.

6. An article comprising glass fibres which have a diameter less than.001 inch and which consist of SiO2 containing 3.1% A1203, .2% B20: and03% Na2O, the fibres being vitreous and nonporous.

7. An article compr'ming glass fibres which have a diameter less than.001 inch and which consist of S102 containing 12% ZrOZ-and 25% Na2O,the fibres bein porous.

8. An article comprising glass fibres which have a diameter less than.001 inch and which consist of Si02 containing 12% ZrOz and 25% Na2O,the fibres being vitreous and non-porous. MARTIN EMERY NORDBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

3. AN ARTICLE COMPRISING GLASS FIBRES WHICH HAVE A DIAMETER LESS THAN .001 INCH AND WHICH CONSISTS ESSENTIALLY OF AT LEAST 88% SIO2, THE INDICATED AMOUNT OF AT LEAST ONE GLASS FLUX SELECTED FROM THE GROUP CONSISTING OF UP TO 1% ALKALI METAL OXIDE AND UP TO 4% B2O3, AND AT LEAST ONE ADDITIONAL GLASS-FORMING OXIDE IN THE INDICATED AMOUNT SELECTED FROM THE CLASS CONSISTING OF UP TO 10% BEO, UP TO 10% MGO, UP TO 10% CAO, UP TO 10% ZNO, UP TO 10% SRO, UP TO 10% CDO, UP TO 10% BAO, UP TO 4% AL2O3, UP TO 12% TIO2, UP TO 12% ZRO2 AND UP TO 12% THO2, THE FIBRES BEING POROUS. 